Late-onset disorders and/or diseases can occur in a variety of physiological systems. For example, neurodegenerative disorders such as Parkinson's disease (PD) or Alzheimer's disease (AD) are becoming a growing burden to society. Higher life expectancies have led to an explosion of the number of individuals diagnosed with those currently incurable and in many cases untreatable disorders. This trend is expected to escalate, as it is estimated that the afflicted population, individuals over 60 years of age, will represent 21.8% of the total world population reaching 2 billion people by 2050. Lutz et al., Nature 451:716-719 (2008).
Age per se is believed by many to be a significant risk factor for neurodegenerative diseases, and it is estimated that, for example, the cases of AD in the U.S. will more than triple from 4 million in 2010 to nearly 14 million by 2050. Hebert et al., Neurology 80(19):1778-83 (2013). Similar increases in incidence are expected for PD over the next 30 years. Dorsey et al., Neurology 68:384-386 (2007). In parallel, therapies for age related disorders such as AD and PD are being developed at an excruciatingly slow rate. Only symptomatic relief is available, limited in terms of both the symptoms treated and the duration of its effectiveness, highlighting the need for novel preventive and therapeutic approaches.
Late-onset neurodegenerative disorders such as Parkinson's disease (PD) are becoming a growing burden to society due to the gradual increase in life expectancy. The incidence of PD will likely continue to rise, as it is estimated that by 2050 21.8% of the projected world population (approximately 2 billion people) will be over 60 years of age (Lutz et al., Nature 451:716-719 (2008).
The use of induced pluripotent stem cell (iPSC) technology where patient-derived skin cells can be reprogrammed back to a pluripotent state and then further differentiated into disease-relevant cell types presents new opportunities for modeling and potentially treating currently intractable human disorders (Bellin et al., Nat Rev Mol Cell Biol 13, 713-726 (2012). However, there is a concern as to how well iPSC-derived cells can model late-onset diseases where patients do not develop symptoms until later in life, implicating age as a necessary component to disease progression.
Several iPSC studies have demonstrated a loss of particular age-associated features during iPSC induction (reviewed in Freije and López-Otin, Curr Opin Cell Biol 24, 757-764 (2012); Mahmoudi and Brunet, Curr Opin Cell Biol 24, 744-756 (2012)). For instance, there is evidence for changes in age-associated features such as an increase in telomere length (Agarwal et al., Nature 464:292-296 (2010); Marion et al., Cell Stem Cell 141-154 (2009)), mitochondrial fitness (Prigione et al., Stem Cells 721-733 (2010); Suhr et al., PloS One e14095 (2010)) and loss of senescence markers (Lapasset et al., Genes Dev 25: 2248-2253, 2011) in iPSCs derived from old donors, suggesting that rejuvenation takes place during old donor cell reprogramming. In addition to the apparent loss of age-associated features in iPSCs, as compared to their primary somatic cell source, another advantage of using iPS cells in progerin aging of iPS derived cells of the present disclosures is the resulting mature phenotype. In contrast, directed differentiation of human pluripotent stem cells (hPSCs) is known to yield immature, embryonic-like cell types, which lack maturation markers and the ability to display late-onset disease phenotypes. In fact, without progerin-induced aging, these immature iPSC-derived cells often require months of in vitro or in vivo maturation to establish robust functional properties of their particular cell type (Liu et al., Curr Opin Cell Biol 24:765-774 (2012); Saha & Jaenisch, Cell Stem Cell 5:584-595 (2009).
Protracted differentiation is thought to reflect the slow timing of human development. For example, human midbrain dopamine (mDA) neurons, the cell type predominantly affected in PD, require months of culture to develop mature physiological behaviors in vitro and months of in vivo maturation to rescue dopamine deficits in animal models of PD (Isacson et al., Trends Neurosci 20:477-482 (1997); Kriks et al., Nature 480:547-551 (2011)). Furthermore, based on the BRAIN-span atlas of the developing human brain (brainspan.org), gene expression data from hPSC-derived neural cells match the transcriptome of first trimester embryos, a stage believed to be too early to model late-onset disorders. These in vitro differentiation data indicated a species-specific intrinsic “clock-like” maturation process that prevented the rapid generation of mature or aged cells posing a major challenge for human iPSC-based modeling of late-onset neurodegenerative disorders such as PD.
A problem in addressing the global aspects of aging and rejuvenation during cell reprogramming and differentiation is the identification of markers that reliably predict the chronological age of the somatic cell donor and the corresponding cellular age of iPSC derivatives.
Induced pluripotent stem cells (iPSCs) have been proposed to be useful for modeling human disease. For example, iPSC technology has been used to study early-onset disorders such as familial dysautonomia or Herpes Simplex encephalitis. Lee et al., Nat Biotechnol 30:1244-1248 (2012); Lee et al., Nature 461:402-406 (2009); and Lafaille et al., Nature 491:769-773 (2012). Discovery of the disease mechanisms for both disorders and high throughput drug screening enabled a human iPSC-based disease model on which screened drug candidates could be further tested.
Despite early progress in modeling early-onset genetic disorders, fundamental questions remain as to how well iPSC-based approaches can model late-onset disorders such as Parkinson's disease (PD) given the embryonic nature of iPSC-derived midbrain dopamine (mDA) neurons. Lee & Studer, Nat Methods 7:25-27 (2010); Saha & Jaenisch, Cell Stem Cell 5:584-595 (2009); and Liu et al., Curr Opin Cell Biol 24:765-774 (2012). Late-onset disorders such as PD take decades to develop without any signs of the disease at early stages of life. Indeed current studies modeling genetic or sporadic forms of PD using iPSC technology show no observed phenotype or display relatively subtle biochemical or morphological changes without recreating the severe degenerative pathology characteristic of the disease. Soldner et al., Cell 146:318-331 (2011); Soldner et al., Cell 136:964-977 (2009); Nguyen et al., Cell Stem Cell 8:267-280 (2011); Seibler et al., J Neurosci 31:5970-5976 (2011); and Cooper et al., Sci Transl Med 4:141ra190 (2012).
The ability to measure and manipulate age in cells differentiated from iPSCs represents a fundamental challenge in pluripotent stem cell research that remains unresolved to date. There has been considerable progress in directing cell fate into the various derivatives of all three germ layers; however, there has been no technology to switch the age of a given cell type on demand from embryonic to neonatal, adult or aged status. This remains a major impediment in the field as illustrated by the persistent failure to generate hiPSC-derived adult-like hematopoietic stem cells, fully functional cardiomyocytes, or mature pancreatic islets and the general inability to derive aged cell types that are age-appropriate and/or stage-appropriate for modeling late-onset diseases.
iPSC models of late-onset disorders such as PD do not adequately reflect the severe degenerative pathology of the disease. Thus, new methods to model late-onset neurodegenerative disorders are needed. Specifically, new methods to generate aged cells that more closely resemble the age of the patient using iPSC technology would be very useful in the quest for effective treatments for late-onset diseases, particularly degenerative ones and more specifically neurodegenerative ones.
Additionally, an ability to accelerate maturation of cells would be useful in providing supplies of age-appropriate cells at a rapid pace, whether for research or therapy.